WO2020089953A1

WO2020089953A1 - Inertization method for materials containing asbestos

Info

Publication number: WO2020089953A1
Application number: PCT/IT2019/050232
Authority: WO
Inventors: Marco GEROLIN; Alberto STEOLO
Original assignee: Friulana Costruzioni S.R.L.
Priority date: 2018-10-31
Filing date: 2019-10-31
Publication date: 2020-05-07
Also published as: IT201800009998A1

Abstract

Inertization method for materials or artefacts containing asbestos, in particular cement-based material containing asbestos, by means of a series of basic and acid reactions.

Description

“INERTIZATION METHOD FOR MATERIALS CONTAINING ASBESTOS”

FIELD OF THE INVENTION

Embodiments described here concern an inertization method for materials or artefacts containing asbestos (MCA), in particular cement-based material containing asbestos.

BACKGROUND OF THE INVENTION

It is known that a series of natural minerals with fibrous morphology belonging to the silicates mineralogical group are indicated by the term asbestos. The chemical structure of silicates is characterized by anionic groups in which a central silicon atom is coordinated to four oxygens in tetrahedral disposition, among which the simplest is the orthosilicate anion with formula [SiO₄]⁴ . These anionic groups associate with different cations, for example iron, manganese, aluminum, calcium and many others. The anionic groups of the silicates can also associate with each other by sharing bridging oxygens between two silicon, forming reticular superstructures.

The two structures that are particularly important in the field of asbestos morphology are the serpentine group, of which the crystalline form most important for our purposes is certainly chrysotile, and amphiboles. The former are characterized by the fact that the silicon and oxygen tetrahedrons are disposed forming layers, in which each silicon shares three oxygens with the adjacent silicon. These layers are alternated with other layers in which cationic species are present in an octahedral conformation. In the case of chrysotile, the latter are formed by Mg oxides-hydroxides. These layers can also form extended sheets, which by curving give rise to tubular or narrow spiral structures, which constitute chrysotile’s base fibril unit, with a diameter typically around 25 nanometers. From a morphological point of view, these chrysotile fibers appear convoluted and flexible.

In the structure of the amphiboles, on the other hand, the silicate groups bond in order to form chains, in which typically two double silicate chains are coordinated by octahedral cations.

From a morphological point of view, the amphibole fibers, which tend to group into bundles, have an acicular, rigid and rectilinear shape, with an average diameter of about 200 nm. An important characteristic of all asbestos is represented by their internal structure, such that from each bundle of fibers it is possible to obtain finer bundles (that is, of the same length but with a smaller diameter). This characteristic differentiates them from other fibrous materials, such as artificial mineral fibers which instead tend to fracture transversely, thus giving rise to shorter fibers, but which have the same diameter. The amphiboles can crystallize in a wide variety of habits: fibrous, asbestiform, prismatic, and others. A mineral crystallizes with a fibrous habit if it is made up of separable fibers; the term asbestiform, on the other hand, has a narrower meaning: the mineral has to resemble an asbestos, and its habit has to possess a series of characteristics including fibrillar structure, flexibility and resistance of the fibers.

Another important characteristic is that all asbestos occur in nature in bundles of long fibers, which are extremely flexible and easily separable from each other.

The fibrous structure confers on asbestos both a remarkable mechanical strength and also a high flexibility; it is also easily spinnable and can be woven and has sound-absorbing and heat-insulating properties. Furthermore, asbestos is non-flammable, resistant to heat and to acid attack, resistant to traction, and easily friable. Asbestos easily bonds with building materials, such as lime, gypsum, cement, and with some polymers, such as rubber or poly vinyl chloride (PVC). These characteristics and its low cost have in the past promoted a wide use of this material in industry, construction and consumer products. In these products, manufactured articles and applications, asbestos fibers can be free or weakly bonded, in which case it is referred to as friable matrix asbestos, or they can be strongly bonded in a stable and solid matrix, such as cement-asbestos or vinyl-asbestos, which is defined as a compact matrix. For example, it has been used to produce fireproof fabrics, fireproof materials, construction materials for the building industry.

It should be noted that if on the one hand the fibrous consistency of asbestos is the basis of its excellent technological properties, on the other hand it gives this material important health risk properties, being the cause of serious pathologies for people, mainly, but not only, for the respiratory system since the fibers can potentially be inhaled. For humans, the inhalation and oral pathways are the main routes of exposure to asbestos, as also indicated in the most recent evaluation of the International Agency for Research on Cancer (I ARC) of the World Health Organization (WHO) - 2012. In 1986, the WHO indicated as dangerous all asbestos fibers with length >5 mpi, diameter <3 pm and size ratio length/diameter >3. The main pathologies caused by asbestos are diseases of the respiratory system, such as asbestosis and lung cancer, and of the serous membranes, mainly the pleura, such as pleural mesothelioma, but also pericardial and peritoneal mesotheliomas. These pathologies occur even after many years after the exposure to asbestos. For example, for these reasons Italy banned asbestos in 1992 with law n. 257. One extremely widespread example of artifacts containing asbestos used for construction are slabs of Etemit, the trade name of a material consisting of a mixture of mortar and asbestos fibers, which used to be used to make accessories in building and road constructions; currently it’s use is forbidden in many countries, including Italy, due to the asbestos fibers harmful to health that are present in it.

The danger of asbestos, in particular, is concrete in those conditions in which material can disperse its fibers in the environment. Asbestos fibers can be released into the atmosphere or into the soil by natural and/or anthropic sources, such as the presence in the area of quarries and mines, landfills, contaminated sites, the movement of rocks and land containing asbestos, as well as the actions of removal, transport and storage (provisional and definitive) of artefacts containing asbestos. Furthermore, another possible source is the considerable presence in the area of artefacts containing asbestos, which with use and aging tend to release fibers into the environment. These sources can cause a dispersion of the fibers with consequent contamination of the environmental matrices in air (i), waters (ii) and soil (iii). The concentration of airborne fibers (i) in the proximity of these possible sources can also be of a few orders of magnitude greater at ground level. With regard to the contamination of surface and underground aquifers (ii), this generally originates from the erosion and leaching of surrounding rocks containing asbestos, or it can be caused by the discharge of wastewater from industrial processes. The presence of asbestos fibers in piped drinking water is instead due to phenomena of erosion/corrosion of pipes made of asbestos-cement. The contamination of the soil (iii), if not of natural origin, is mainly attributable to the presence of illegally stored waste containing asbestos. Considering on the one hand the widespread use, particularly in the past, of materials containing asbestos in industry, construction and consumer products, and on the other hand the proven harmful effects of asbestos on health, it has become necessary to implement decontamination measures able to reduce the environmental impact of products and artefacts containing asbestos present in the environment, whether internal or external. These decontamination measures can essentially be of the physical, thermal or chemical type. Physical type measures are primarily: removal of asbestos, materially eliminating the source of the risk, encapsulation by means of impregnation with penetrating or covering products that protect the external surface, and confinement, by means of installation of sealed barriers, in order to separate and isolate asbestos from the environment. However, although these decontamination measures postpone the problem in time, they do not solve it definitively, since as a matter of fact, since the asbestos is not rendered inert, its intrinsic danger is maintained, limiting only its effects on the environment.

Thermal type measures exploit the intrinsic instability of the asbestos fibers at high temperatures (e.g. chrysotile decomposes at around 800°C) and/or vitrification processes, however they require considerable investments and costs for industrial implementation and use, due to the need to use for example furnaces or plasma technologies.

Chemical type measures known so far are mainly based on acid or alkaline treatments, with acids/bases that are industrially prepared or originate from waste products from other workings, or from carbonation, or which are electrochemical. The disadvantages associated with chemical treatments are primarily related to the fact that when they are used on a large scale, they require large quantities of reagents, causing further environmental risks, and significant costs related to the purchase of reagents and to the disposal of the reaction products. Furthermore, at the end of the known chemical treatments there is always a solid residue which constitutes a hazardous waste. In some cases, physical, thermal and chemical methods can be combined together. In any case, the known methods set out to obtain a solid material free of asbestos or with inert asbestos.

There is therefore the need to perfect an inertization method for materials containing asbestos that can overcome at least one of the disadvantages of the state of the art.

In particular, one purpose of the present invention is to perfect a method which allows to bring into solution all the components of the starting solid material in which asbestos is present, obtaining a closed circuit regarding the residual solid component of the material treated.

The Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages.

Other limitations and disadvantages of conventional solutions and technologies will be clear to a person of skill after reading the remaining part of the present description with reference to the drawings and the description of the embodiments that follow. It is clear that the description of the state of the art connected to the present description must not be considered an admission that what is described here is already known from the state of the prior art.

SUMMARY OF THE INVENTION

The present invention is set forth and characterized in the independent claim, while the dependent claims describe other characteristics of the invention or variants to the main inventive idea.

According to some embodiments, an inertization method for materials containing asbestos is provided. According to one embodiment, the method as above comprises the following steps:

i) making available a powder of materials containing asbestos;

ii) reacting said powder in water with an aqueous solution of a first inorganic acid agent;

iii) neutralizing the pH of the mass reacted in ii);

iv) filtering the reacted mass neutralized in iii), obtaining a first solid filtered mass and a first permeated liquid flow;

v) reacting in a hot condition said first solid filtered mass in water with an inorganic basic agent;

vi) neutralizing the pH of the mass reacted in v);

vii) filtering the reacted mass neutralized in vi), obtaining a second solid filtered mass and a second permeated liquid flow;

viii) reacting in a hot condition said second solid filtered mass in water with an aqueous solution of a second inorganic acid agent;

ix) neutralizing the pH of the mass reacted in viii);

x) filtering the reacted mass neutralized in ix), obtaining a third solid filtered mass and a third permeated liquid flow;

(xi) reacting in a hot condition said third solid filtered mass in water with an inorganic basic agent;

xii) neutralizing the pH of the mass reacted in xi);

xiii) filtering the reacted mass neutralized in xii), obtaining a fourth residual solid filtered mass and a fourth permeated liquid flow;

xiv) recirculating in step ii) said fourth residual solid filtered mass to react with said aqueous solution of the first inorganic acid agent together with said powder in water, so that said inertization method is in a closed cycle with respect to the residual solid mass.

Advantageously, the method according to the aspects described here provides, after the reaction ii), an alternation of other basic v) and xi) and acid viii) hydrothermal reactions, with the possible reintroduction of the residual solid material at the end of the process into a subsequent working batch, or possibly storage and reprocessing at dedicated moments, and with the aim of obtaining a closed circuit with respect to the residual solid component of the material treated. Substantially, the method according to the aspects described here, differently from known methods, allows to bring into solution all the various components of the starting solid material, except for insoluble fractions in the different reaction conditions, which in any case asbestos is not present.

Moreover, the method in accordance with the aspects described here is also advantageous from a recycling and recovery perspective, since the acid solutions used can also come from wastewater of industrial workings, for example acid solutions deriving from the surface treatment of metals, usually hydrochloric or sulfuric acid.

These and other aspects, characteristics and advantages of the present disclosure will be better understood with reference to the following description, drawings and attached claims. The drawings, which are integrated and form part of the present description, show some embodiments of the present invention, and together with the description, are intended to describe the principles of the disclosure.

The various aspects and characteristics described in the present description can be applied individually where possible. These individual aspects, for example aspects and characteristics present in the description or in the attached dependent claims, can be the object of divisional applications.

It is understood that any aspect or characteristic that is discovered, during the patenting process, to be already known, shall not be claimed and shall be the object of a disclaimer.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other characteristics of the present invention will become apparent from the following description of some embodiments, given as a non-restrictive example with reference to the attached drawings wherein:

- Fig. 1 shows the infrared absorption spectra respectively for a sample of MCA upstream of the process (untreated, indicated as L3 in the legend) and of the solid material remaining downstream of the treatment (12, 14 and 15 in the legend);

- Fig. 2 shows SEM images of MCA upstream of the treatment for the material subjected to pulverization only: (a) 500x, (b) 2000x, (c) 5000x and downstream of the treatment: (d) 500x, (e) 2000x, (f) 5000x;

- Fig. 3 shows an SEM (Scanning Electron Microscopy) image (a) and the EDS (Energy Dispersive X-Ray Spetroscopy) spectra (b, c, d) for MCA upstream of the treatment and an SEM image (e) and the EDS spectra (f, g, h) for MCA downstream of the treatment;

- Fig. 4 shows the distribution of the elemental composition (expressed as oxides) of (a) untreated MCA and (b) residual material downstream of the treatment; - Fig. 5 shows SEM images of MCA subjected to wet grinding, with the following enlargements: (a) 200x, (b) 500x, (c) lOOOx, (d) 2000x.

DETAILED DESCRIPTION OF SOME EMBODIMENTS

We will now refer in detail to the various embodiments of the present invention, of which one or more examples are shown in the attached drawings. Each example is supplied by way of illustration of the invention and shall not be understood as a limitation thereof. For example, the characteristics shown or described insomuch as they are part of one embodiment can be adopted on, or in association with, other embodiments to produce another embodiment. It is understood that the present invention shall include all such modifications and variants.

Before describing these embodiments, we must also clarify that the present description is not limited in its application to details of the construction and disposition of the components as described in the following description using the attached drawings. The present description can provide other embodiments and can be obtained or executed in various other ways. We must also clarify that the phraseology and terminology used here is for the purposes of description only, and cannot be considered as limitative.

Unless otherwise defined, all the technical and scientific terms used here and hereafter have the same meaning as commonly understood by a person with ordinary experience in the field of the art to which the present invention belongs. Even if methods and materials similar or equivalent to those described here can be used in practice and in the trials of the present invention, the methods and materials are described hereafter as an example. In the event of conflict, the present application shall prevail, including its definitions. The materials, methods and examples have a purely illustrative purpose and shall not be understood restrictively.

All percentages and ratios indicated are intended as referring to the weight of the total composition (w/w), unless otherwise indicated.

All the percentage intervals reported here are provided with the provision that the sum with respect to the overall composition is 100%, unless otherwise indicated.

All the intervals reported here shall be understood to include the extremes, including those that report an interval“between” two values, unless otherwise indicated.

The present description also includes the intervals that derive from uniting or overlapping two or more intervals described, unless otherwise indicated.

The present description also includes the intervals that can derive from the combination of two or more values taken at different points, unless otherwise indicated.

Embodiments described here concern an inertization method for materials containing asbestos. The method as above comprises the following steps: i) making available a powder of materials containing asbestos;

iii) neutralizing the pH of the mass reacted in ii);

vi) neutralizing the pH of the mass reacted in v);

ix) neutralizing the pH of the mass reacted in viii);

xii) neutralizing the pH of the mass reacted in xi);

With the terms “inertization” or “inerting” here and in the following description we mean the subjecting of materials containing asbestos to treatments or transformations able to make them non-hazardous.

In accordance with some embodiments, combinable with all the embodiments described here, the materials containing asbestos as above are cement-based materials containing asbestos, comprising, in a dry state, from 45 to 75% in weight, in particular from 50 to 70% in weight, of calcium carbonate, from 5 to 25% in weight, in particular from 10 to 20% in weight, of asbestos and from 20 to 50% in weight, in particular from 25 to 45% in weight, of silica, except for possible impurities present. A possible example provides that the materials containing asbestos as above comprise about 60% in weight of calcium carbonate, about 15% weight of asbestos and about 35% in weight of silica, except for possible impurities present.

In some embodiments, combinable with all the embodiments described here, the method as above provides to identify or know in advance the percentage content in weight of at least calcium carbonate or calcium hydroxide, asbestos and silica in the materials containing the asbestos to be treated. Advantageously, this can be carried out in a programmed manner for a given type of material, after which the parameters of the treatment described here can be adjusted accordingly and the method according to the embodiments described can be implemented in an efficient and productive manner. For example, when confronted with a homogeneous type of material to be treated, for example having the same origin, it is possible to carry out a sample analysis in order to know in fact the percentage content in weight at least of calcium carbonate or calcium hydroxide, asbestos and silica in the materials containing the asbestos to be treated, and consequently calibrate the process parameters to be used to inert the specific type of material until it is exhausted. After which, with a new batch or set of batches of material to be treated, for example of different origin or type, it will be possible to carry out the analysis again in order to characterize its percentage content in weight at least of calcium carbonate or calcium hydroxide, asbestos and silica and proceed with the calibration of the process parameters for the new batch or set of batches of material to be treated.

Moreover, the method according to some embodiments provides to:

- meter water in steps ii), v), viii) and xi) and an aqueous solution of the first and second inorganic acid agent respectively in steps ii) and viii) and inorganic basic agent in steps v) and xi) in ratio with an initial dry mass of powder of materials containing asbestos made available in step i);

- define, as a function of said percentage content in weight of calcium carbonate or calcium hydroxide, the weight ratios to be used in step ii) between dry mass of powder of materials containing asbestos made available in step i) and water used in step ii), and between dry mass of powder of materials containing asbestos made available in step i) and aqueous solution of first inorganic acid agent used in step ii);

- define, as a function of said percentage content in weight of silica, the weight ratios to be used in step v) and in step xi) between dry mass of powder of materials containing asbestos made available in step i) and water used in step v) and in step xi), and between dry mass of powder of materials containing asbestos made available in step i) and inorganic basic agent used in step v) and in step xi);

- define, as a function of said percentage content in weight of asbestos, the weight ratios to be used in step xi) between dry mass of powder of materials containing asbestos made available in step i) and water used in step viii), and between dry mass of powder of materials containing asbestos made available in step i) and aqueous solution of the second inorganic acid agent used in step viii).

In order to identify the composition of the starting material to be treated, embodiments of the method, combinable with all the embodiments described here, provide a preliminary step of scanning electron microscopy (SEM) analysis of said materials containing asbestos, initially before making available said powder of materials containing asbestos made available in step i), in order to determine the composition of the material, identifying the percentage content in weight at least of calcium carbonate or calcium hydroxide, asbestos and silica.

In some embodiments, combinable with all the embodiments described here, in step ii) the weight ratio between dry mass of powder of materials containing asbestos made available in step i) and water ranges from 1 :0.5 to 1 :2, in particular from 1 :0.8 to 1 : 1.2. A possible example of weight ratio is 1 : 1.

In some embodiments, combinable with all the embodiments described here, in step ii) the weight ratio between dry mass of powder of materials containing asbestos made available in step i) and aqueous solution of first inorganic acid agent ranges from 1 :1 to 1 :2, in particular from 1 : 1.1 to 1 :1.7. A possible example of weight ratio is 1 : 1.45.

In other embodiments, combinable with all the embodiments described here, in step v) and in step xi) the weight ratio between dry mass of powder of materials containing asbestos made available in step i) and water ranges from 1 : 10 to 1 :2, in particular from 1 :7 to 1 :3. A possible example of weight ratio is 1 :5. In other embodiments, combinable with all the embodiments described here, in step v) and in step xi) the weight ratio between dry mass of powder of materials containing asbestos made available in step i) and inorganic basic agent ranges from 1 :1 to 1 :0.05, in particular from 1 :0.8 to 1 :0.1. A possible example of weight ratio is 1 :0.15.

In other embodiments, combinable with all the embodiments described here, in step viii) the weight ratio between dry mass of powder of materials containing asbestos made available in step i) and water ranges from 1 : 10 to 1 :2 , in particular from 1 :7 to 1 :3. A possible example of weight ratio is 1 :5.

In other embodiments, combinable with all the embodiments described here, in step viii) the weight ratio between dry mass of powder of materials containing asbestos made available in step i) and aqueous solution of second inorganic acid agent ranges from 1 :0.1 to 1 :0.5, in particular from 1 :0.11 to 1 :0.3. A possible example of weight ratio is 1 :0.170.

In possible implementations, the materials containing asbestos as above to be subjected to treatment can be in the form of sheets or pipes of material, in particular cement-based material, containing asbestos (asbestos-cement composite, for example Etemit).

In accordance with some embodiments, combinable with all the embodiments described here, step i) provides to subject the materials containing asbestos to coarse grinding and thereafter to a fine comminution. Advantageously, in this way a powder is obtained with a D₈₀ granulometry not higher than 700 pm, in particular equal to or less than 500 pm which is made available in step i).

In accordance with some embodiments, combinable with all the embodiments described here, the powder of materials containing asbestos made available in step i) is in the presence of water, in order to supply it in wet form to the subsequent step ii).

In accordance with some embodiments, combinable with all the embodiments described here, the fine comminution can be carried out dry, for example by means of a hammer mill, or wet, for example by means of a ball mill.

In the event the comminution is carried out dry, the association of the powder of materials containing asbestos with water is carried out by means of wetting. In this case, the wetting weight ratio used between powdered solid and water is about 1 :1. For example, a humidifying Archimedes screw can be used for the wetting.

In the event the fine comminution is carried out wet, the association of the powder of materials containing asbestos with water may also not be carried out by means of wetting, if the dilution ratio used in the wet grinding is suitable and already stands at about a ratio between powdered solid and water of about 1 :1.

The powder obtained after the fine comminution is transported by means of a pneumatic transport device up to a collection hopper, possibly wetted by means of the humidifying Archimedes screw as indicated above in the case of dry fine comminution, and then fed to a storage tank provided with a suitable mixing device.

Consequently, in embodiments described here, preliminarily the material is subjected to a treatment of the physical type, which includes at least the coarse grinding and subsequent fine comminution operations as above, with possible wetting in the case of dry comminution. The powder of materials containing asbestos which is obtained is therefore the one made available in step ii).

Furthermore, in the embodiments described here, the subsequent steps from ii) to xiv) fall within the scope of a chemical treatment of the powder of materials containing asbestos. This chemical treatment is in turn subdivided into a decarbonation treatment, which comprises steps from ii) to iv) and a hydrothermal treatment, which comprises steps from v) to xiv). The hydrothermal treatment in fact includes, as described above, three successive reactions, basic (step v)), acid (step viii)) and again acid (step xi)), the respective neutralizations (steps vi), ix) and xii)) and filtrations (steps vii), x) and xiii)).

Preferably, the reaction steps ii), v), viii) and ix) as above, and the associated neutralization steps are carried out in reaction environments, that is, reactors, distinct and separate from each other.

In some embodiments, the decarbonation treatment according to steps from ii) to iv) provides the step ii) of reaction between calcium carbonate, or possibly residual calcium oxide/hydroxide, contained in the powder of material to be treated, and aqueous solution of first organic acid agent as above. This reaction, which in effect carries out the decarbonation, is typically a very rapid reaction, with development of heat (exothermic reaction) and evolution or emission of gaseous carbon dioxide, as explained below.

It should be noted that, as a function of the age of the material containing asbestos that is being treated, the quantity of calcium carbonate present in the material containing asbestos increases over time as the age of the material itself increases. In fact, calcium carbonate can be replaced by calcium oxide/hydroxide, since calcium carbonate is progressively formed with the carbonation reaction of calcium oxide/hydroxide in contact with carbon dioxide present in the air.

The first organic acid agent as above can be, for example, hydrochloric acid. For example, as an aqueous solution of the first organic acid agent it is possible to use technical hydrochloric acid, which is defined as an aqueous solution of hydrochloric acid at 30-33% m/m of hydrochloric acid in water.

In the hypothesis of using hydrochloric acid in aqueous solution, in the case of calcium carbonate the decarbonation reaction is therefore:

CaCO_3(s) + 2 HCl_(aq)- CaCl_2(aq) + H₂O_(i) + CO_2(g) while in the case of calcium hydroxide the decarbonation reaction is:

For example, in the event the material containing asbestos to be treated initially contains, in a dry state, about 60% in weight of calcium carbonate, then the weight ratio between dry mass of powder of materials containing asbestos and aqueous solution of hydrochloric acid is 1.5 in mass.

This step ii) is typically carried out in a first dedicated acid reaction reactor. This first reactor is a closed reactor, suitable to withstand the reaction conditions in an acid environment and, in addition, the temperature increase resulting from the exothermic reaction in question. Furthermore, the first reactor is equipped with a stirring device. In addition, the first reactor is equipped with a device to capture the gaseous carbon dioxide that develops from the reaction, in order to capture the gaseous carbon dioxide and convey it toward an outlet. The evolution or emission of gaseous carbon dioxide, together with the development of heat, also generates foam in the reactor, and also for this reason the reactor used is of the closed type. Moreover, precisely because of the generation of foam, the aqueous solution of the first inorganic acid is progressively metered in the first reactor, in order to keep the foaming effect under control.

Advantageously, in order to reduce the foaming effect, the pressure which is maintained inside the first reactor is lower than atmospheric pressure. In other words, the first reactor is kept in slight depression, to limit the formation of foam.

The first reactor is preferably equipped with a device to measure pH (pH meter), a temperature sensor and a flow meter to detect the flow of gaseous carbon dioxide that passes through the device to capture the carbon dioxide.

The typical duration of the reaction with the aqueous solution of the first inorganic acid as in step ii) is from 1 hr to 3 hr, in particular from 1.5 hr to 2.5 hr. A typical example of the duration of step ii) is 2 hr.

In possible embodiments, the end of reaction of step ii) is determined when all the following three conditions occur:

- pH below 3 for over 15 minutes;

- temperature inside the reactor decreasing even after further additions of the aqueous solution of the first inorganic acid;

- cessation of the emission of carbon dioxide even after further additions of the aqueous solution of the first inorganic acid.

Advantageously, this decarbonation treatment has the purpose of effecting the dissolution of calcium carbonate or possible calcium hydroxide present in the material containing the initial asbestos.

At the end of the reaction of step ii), the step iii) of neutralizing is carried out, to bring the system to neutral pH, for example with sodium hydroxide or calcium hydroxide (lime water), typically in aqueous solution. Thereafter, the step iv) of filtration is carried out, which for example can be a filtration at 5 pm. The residual solid phase is fed to the subsequent hydrothermal treatment, in particular to step v). Instead, the filtered solution can for example be subjected to concentration by means of evaporation of the aqueous solution of calcium chloride (CaCl₂) for example for commercial purposes, or, alternatively, it can be subjected to selective precipitation in a basic environment to again obtain Ca(OH)₂, usable for example in construction as a lime for painting or other.

In other embodiments, the subsequent hydrothermal treatment as in steps from v) to xiii) provides the first basic reaction v), neutralization vi) and then filtration vii).

The reaction of step v) is a reaction in a hot condition in a basic environment to which the solid residue obtained from the step iv) of filtration is subjected, and which provides the reaction between the silica present, originally contained in the powder of the material to be treated, and inorganic basic agent.

The basic agent as above can be, for example, solid sodium hydroxide and, in this case, the reaction is:

2 NaOH_(aq) + Si0_2(s)^Na₂Si03_(aq) + H₂0_(i)

In particular, to the filtered and washed solid residue obtained from step iv) are added water with a solid/liquid ratio from 1 :2 to 1 : 10, in particular from 1 :3 to 1 :8, for example 1 :5, and solid sodium hydroxide in order to exploit the exothermic properties of the dissolution reaction.

In this specific case, if the material containing asbestos to be treated initially contains, in a dry state, about 35% in weight of silica, the solid sodium hydroxide which is used in step v) is from about 40% to about 60%, for example about 50%, of the weight of silica originally contained in the initial material containing dry asbestos: for example, for each ton of material containing dry asbestos initially provided upstream of the process, in this step v) about 130 kg of solid sodium hydroxide are fed. In general, the SiO₂/NaOH ratio affects the Si0₂/Na2O ratio of the final sodium silicate solution. Therefore, the completed reaction as indicated by way of example above is obtained with a SiO₂/NaOH ratio equal to about 1 : 1.3. This ratio can also vary as a function of the commercial purpose of the resulting solution.

Alternatively, it is also possible to use concentrated aqueous solutions of sodium hydroxide, as long as the desired Si0₂/NaOH ratio is maintained.

This reaction, which effectively dissolves the silica, is typically a reaction that requires heat and is generally carried out at a temperature from 200 °C to 250 °C and a pressure corresponding to the vapor pressure at the given temperature, which can for example be of about 40 bar.

This step v) is typically carried out in a second dedicated basic reaction reactor. This second reactor is a closed reactor, suitable to withstand the reaction conditions in basic environment and, in addition, the temperature required for the reaction in question. Furthermore, the second reactor is equipped with a stirring device.

The second reactor is preferably equipped with a device to measure pH (pH meter), a temperature sensor and also a pressure sensor. The typical duration of the reaction with the inorganic basic agent as in step v) can be from 2 hr to 6 hr, in particular from 3 hr to 6 hr. A typical example of duration of step v) is 4 hr, or more, even up to 6 hours.

Advantageously, this basic reaction in a hot condition has the function of dissolving the silica present in the material and bringing it into solution: in this specific case, the sodium hydroxide attacks the silica and brings it into solution as sodium silicate. The high temperature of the reaction, from 200 °C to 250 °C, advantageously also has the function of dissolving the sodium silicate and bringing it into solution. In this way, at least part of the original silica is removed into solution with the liquid phase. It is also possible to remove all the original silica in this step, increasing the reaction time and adding other water and possibly another basic agent.

At the end of the reaction of step v), the reaction environment is cooled and the step vii) of neutralizing with an inorganic acid agent is carried out, in order to bring the system to neutral pH. After which, the step vii) of filtration is carried out, which for example can be a filtration at 5 pm. The residual solid phase is fed to the subsequent acid reaction as in step vii). Instead, the filtered solution can for example be subjected to the recovery of the dissolved sodium silicate by means of concentration by evaporation of the water. Alternatively, the dissolved sodium silicate can be recovered by precipitation in an acid environment, for example using sulfuric acid:

Na₂Si0_3(aq) + H₂S0_4(aq) ^Si0_2(s) + Na₂S0_{4 (aq)} + H₂0_(l)

In other embodiments, the hydrothermal treatment as in steps from v) to xiii) provides the second acid reaction viii), filtration ix) and then neutralization x).

The reaction of step viii) is a reaction in a hot condition in an acid environment to which the solid residue obtained from the step vii) of filtering is subjected, and which provides the reaction between the asbestiform component, originally contained in the powder of material to be treated, and the aqueous solution of the second inorganic acid agent.

In possible implementations, the second inorganic acid agent of step viii) is an acid chosen from a group consisting of: phosphoric acid, hydrochloric acid, sulfuric acid, nitric acid, hydrobromic acid. For example, sulfuric acid in aqueous solution at 95% m/m can be used as an aqueous solution of second inorganic acid agent. For example, if using sulfuric acid in aqueous solution at 95% m/m, the weight ratio between dry mass of powder of materials containing asbestos made available in step i) and aqueous solution of sulfuric acid in aqueous solution at 95% m/m is 1 :0.170.

The reactions involved are different, based on the type of inorganic acid used and the type of asbestos to be treated, that is, whether serpentines or amphiboles. For example, if using phosphoric acid, the following reactions occur:

- serpentines:

Mg₃(Si₂0₅)(0H)_4(s) + 6H₃P0_4(aq)^3Mg(H₂P0₄)_2(S) + 5H₂0₍₁₎+ Si0_2(s)

- amphiboles

Ca₂Mg₅Si₈0₂₂(0H)_2(s) + l4H₃P0_4(aq)^2Ca(H₂P0₄)₂ + 5Mg(H₂P0₄)₂ + 8H₂0_(I) + 8Si0_2(S)

For example, if using hydrochloric acid, the following reactions occur:

- serpentines:

Mg₃(Si₂0₅)(0H)_4(s) + 6HCl_(aq)- 3MgCl_2(aq) + 5H₂0₍₁₎+ Si0_2(s)

- amphiboles:

Ca₂Mg₅Si₈0₂₂(0H)_2(S) + l4HCl_(aq) ^2CaCl_2(aq) + 5MgCl_2(aq) + 8H₂0_(i) + 8Si0_2(S)

For example, if using sulfuric acid, the following reactions occur:

- serpentines:

Mg₃(Si₂0₅)(0H)_4(S) + 3H₂S0_4(aq)^3MgS0_4(aq) + 5H₂0_(i)+ Si0_2(s)

- amphiboles:

Ca₂Mg₅Si₈0₂₂(0H)_2(s) + 7H₂S0_4(aq))^2CaS0_4(aq) + 5MgS0_4(aq) + 8H₂0₍₁₎+ 8Si0_2(s) These reactions are indicated in general terms, considering the heterogeneity of the starting material. Moreover, if phosphoric acid is used, we believe that, given the high temperatures that characterize this step viii) (about 200 °C - 250 °C as explained below), the dissociation of the phosphoric acid is completed, obtaining the di-, mono- and tri-basic phosphates of the corresponding alkaline earth metals.

In particular, water is added to the filtered and washed solid residue obtained from step vii) with a solid/liquid ratio from 1 :2 to 1 : 10, in particular from 1 :3 to 1 :8, for example 1 :5.

In this specific case, if the material containing asbestos to be treated initially contains, in a dry state, about 15% in weight of asbestos, the quantity of aqueous solution of sulfuric acid which is used in step viii) is approximately equal to, or slightly more than, the weight of asbestos originally contained in the initial material containing dry asbestos: for example, for each ton of material containing dry asbestos initially provided upstream of the process, in this step viii) about 168 kg of aqueous solution of sulfuric acid are fed.

This reaction, which for all intents and purposes attacks and dismantles the asbestos fibers, bringing into solution the magnesium and effectively leaving only the silicon skeleton, is typically a reaction that requires heat and is generally carried out at a temperature of 200 °C to 250 °C and a pressure corresponding to the vapor pressure at the given temperature, which for example can be of about 40 bar.

This step viii) is typically carried out in a dedicated third acid reaction reactor. This third reactor is a closed reactor, suitable to withstand the reaction conditions in acid environment and, in addition, the temperature required for the reaction in question. Furthermore, the third reactor is equipped with a stirring device.

The third reactor is preferably equipped with a device to measure pH (pH meter), a temperature sensor and also a pressure sensor.

The typical duration of the reaction with the inorganic basic agent as in step viii) can be from 2 hr to 6 hr, in particular from 3 hr to 6 hr. A typical example of duration of step viii) is 4 hr, or longer, even up to 6 hours.

Advantageously, this acid reaction in a hot condition has the function of dismantling the magnesium hydroxide, which is brought into solution. In this way, with the liquid phase the magnesium of the magnesium hydroxide of the asbestiform component is removed into solution.

At the end of the reaction of step viii), the reaction environment is cooled and the step ix) of neutralizing with an inorganic basic agent is carried out, in order to bring the system to a neutral pH, for example using sodium hydroxide or lime water. After which, the step x) of filtering is carried out, which for example can be a filtration at 5 pm. The residual solid phase is fed to the subsequent basic reaction as in step xi). Instead, the filtered solution can for example be subjected to the recovery of the metal salts, for example magnesium, calcium and iron, as a function of the acid used. Alternatively, the various metals can be obtained in the form of hydroxides by precipitation in an alkaline environment. In other embodiments, the hydrothermal treatment as in steps from v) to xiii) provides the second basic reaction xi), neutralization xii) and then filtration xiii), which are analogous to the steps of first basic reaction v), neutralization vi) and then filtration vii), described above.

The basic reaction of step xi) is, similarly to the first step of basic reaction v), a reaction in a hot condition in a basic environment to which the solid residue obtained from the step x) of filtering is subjected, and which has the purpose of removing part of the silica component that has formed following the reaction viii) with the second inorganic acid agent due to disintegration of the fibrous matrix of the asbestos following the reactions discussed above.

In this specific case, if the material containing asbestos to be treated initially contains, in a dry state, about 35% in weight of silica, the solid sodium hydroxide which is used in step v) is about 40% to about 60%, for example about 50%, of the weight of silica originally contained in the material containing initial dry asbestos: for example, for each ton of material containing dry asbestos initially provided upstream of the process, in this step v) about 100 kg of solid sodium hydroxide are fed. Therefore, the completed reaction as indicated above by way of example is obtained with a SiO₂/NaOH ratio equal to about 1 :1. Also in this case, this ratio can vary also as a function of the commercial purpose of the resulting solution.

What described in relation to the step of basic reaction v) applies to the operative and reaction conditions of the step of basic reaction xi); briefly, the reaction occurs at a temperature from 200 °C to 250 °C and a pressure corresponding to the vapor pressure at the given temperature, which for example can be of about 40 bar, in a fourth dedicated basic reaction reactor. This fourth reactor is also a closed reactor, suitable to withstand the reaction conditions in basic environment and, in addition, the temperature required for the reaction in question. Furthermore, the fourth reactor is also equipped with a stirring device. The fourth reactor is also preferably equipped with a device to measure pH (pH meter), a temperature sensor and also a pressure sensor.

The typical duration of the reaction with the inorganic basic agent as in step xi) can be from 2 hr to 6 hr, in particular from 3 hr to 6 hr. A typical example of duration of step xi) is 4 hr, or longer, even up to 6 hours.

After the neutralization xii) and filtration xiii), the residual solid phase is recirculated directly, or after having been suitably stored at step ii), to the subsequent acid reaction as in step vii) to react with the aqueous solution of the first inorganic acid agent together with the powder in water, so that the inertization method according to the embodiments described here is in a closed cycle with respect to the residual solid mass. In other words, the method described here does not provide any residual solid mass whatsoever at exit from the treatment cycle.

Advantageously, therefore, at the end of the treatment according to the method described here, the solid residual material can be equal to about 10% (or less) of the quantity introduced upstream of the treatment. This residue can be introduced in a subsequent batch to be sent to the reaction of step ii) or stored separately and processed in dedicated moments, always being recirculated or re-introduced in step ii).

The method according to the present description, therefore, obtains a closed cycle reducing to zero (or to the insoluble minimum) the quantity of solid material to be disposed of. In particular, advantageously the different materials making up the material containing asbestos (MCA) are progressively brought into solution, thus eliminating the intrinsic danger of asbestos, the problems deriving from its disposal, also allowing to obtain new raw materials (such as calcium chloride, precipitated silica, sodium silicate, and salts of the metals that previously constituted the asbestos).

EXPERIMENTAL DATA

Infrared spectroscopy in Fourier transform

Fig. 1 shows the infrared absorption spectra respectively for a sample of material containing asbestos (MCA) upstream of the process (therefore untreated, indicated in the legend as L3) and of the solid material remaining downstream of the treatment (in the legend as 12, 14 and 15).

In general, it should be noted that the zone around 3500 cm ¹ and 1500-1700 cm ¹ are respectively typical zones of stretching and bending of the OH group. The line widening which leads to a partial (or at times) complete covering of other signals is due mainly to the formation of hydrogen bridges, for example Si- O— H— OH2, Si-O— H— O-Si. This phenomenon is therefore an indication of an increase in the number of free hydroxyl groups (OH) available for the formation of hydrogen bridges, which can be interpreted as an increase in the number of O- Si-O chains, deriving precisely from the destruction of the fibrous component and the liberation of new SiO₂ groups. It should also be noted that the widened shape of the absorption bands can depend on the availability of new Si-OH groups and the consequent formation of new hydrogen bridges, which can increase the quantity of water adsorbed.

We have observed that the decarbonation treatment is completely effective, as evidenced by the disappearance of the absorption bands at 1.383 and 1.460 cm ¹ typical of the carbonate ion. This signal disappearance is indicative of the complete dissolution of the matrix encapsulating the fibers, thus making the latter available for subsequent inertization processes.

We have also noted that the spectra of the treated samples are without the absorption shoulder typical of asbestiform silicates, whose analytical signals are located at 3.655 and 3.686 cm ¹.

The peak at 1.638 cm ¹ then indicates a strong increase of the quantity of surface water adsorbed on the silicate, from which it is possible to deduce a corresponding strong increase of the available surface, indicative of fibrous disintegration.

Further proof comes from the strong absorption band located in the region 1,000-1,200 cm ¹ typical of the stretching of free Si-OH. The fact that this absorption peak is so widened is indicative of a dimensional distribution deriving from the disintegration of the fibers (signal absent in the L3 sample).

The signal at 800 cm ¹ is finally associated with the silica deformation mode, as well as the widening of the absorption below 600 cm ¹, typical of Si-OH vibrations.

The disappearance of the absorptions typical of asbestiform phyllosilicates and the simultaneous birth of signals typical of siliceous/glassy materials confirm the effectiveness of the inertization process, which has led to the transformation of the asbestos fibers into a non-crystalline form of hydrated silica.

Scanning electron microscopy Fig. 2 shows the images in scanning electron microscopy (SEM) of MCA samples upstream of the treatment, subjected to comminution or pulverization only, at (a) 500, (b) 2000, (c) 5000 enlargements and downstream of the treatment at (d) 500, (e) 2000, (f) 5000 enlargements. We can observe the absence of fibrous components typical of asbestiform minerals, and a homogeneous distribution of material in amorphous or micro/nanocrystalline phase.

In addition to the characterization based only on morphological observation, scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM/EDS) allows a precise qualitative and quantitative determination of the composition of the material under examination. In the SEM/EDS analysis, the evaluation of the asbestos is first carried out verifying its fibrous habit (via SEM) and then the EDS spectroscopy allows a univocal characterization of the type of material.

Fig. 3 shows the SEM/EDS spectra for MCA upstream (a, b, c, d) and downstream (e, f, g, h) of the treatment (after steps xi), xii), xiii) of the second basic reaction). The panels b), c), d) of fig. 3 are the EDS spectra of the spots indicated in the image of the panel a), while the panels f), g) and h) are the spectra of the spots indicated in the image of the panel e). The three spots selected upstream and downstream of the treatment refer to three different points of the material. First of all, comparing the SEM images of fig. 3 a) and e), we observe the disappearance of the fibrous habit following the treatment.

Turning to the EDS spectra, in the asbestiform materials, in particular serpentine (the most common form of asbestos), the ratio between the peaks of Mg and Si varies between 0.9 and 1.1 ; in general, the spectral characteristics usually used to identify the fibrous structures are that: the peaks of Mg and Si are in a ratio Mg/Si 0.7- 1.1 (chrysotile); Si and Fe are visible and clearly distinguishable from the background signal (crocidolite and amosite); Mg, Si, Ca (tremolite) are sufficiently evident above the bottom. On the basis of these characteristics, the comparison between the spectra 3 b), c) and d) and 3 f), g) and h) confirms the effectiveness of the method developed.

In particular, in the spectra f), g) and h), we observe how the peaks at 1.25 and 1.73 KeV, respectively typical of the ka line of Mg and Si show a heavily unbalanced relative intensity, in a maximum ratio observed around 0.1, as proof of the fibrous disintegration of asbestos (as already observed in fig. 2, panels d), e), f)). The small component of Mg remaining is to be attributed to residual MgO since it is insensitive to the treatment in alkaline environment.

X-ray fluorescence

In fig. 4, a) and b), we show the diagrams of the elemental compositions of the material before (a) and after (b) the treatment, derived from characterization by means of X-ray fluorescence (XRF). This technique allows to obtain a qualitative and quantitative determination of the chemical species present as a mean distribution over the entire sample, similarly to SEM/EDS which however provides punctual information. The fact that the elementary composition in the diagrams of fig. 4, a) and b) is reported only in terms of the elements present indicated as oxides, depends on the fact that there is no structural information in this type of analysis. Fig. 4 shows the comparison between the composition of the MCA at entry and of the residual material at exit downstream of the treatment. In particular, fig. 4 shows the distribution of the elemental composition (expressed as oxides) of (a) untreated MCA and (b) residual material downstream of the treatment. It should be noted that the quantity of CaCO₃ was determined by means of calcimetry and corrected in the CaO signal in order to avoid double determinations.

We have observed that following the treatment, the residual composition is essentially given by silica (Si0₂) and by the insoluble compounds of Mg. In this specific case, we report the example of a treatment in which the step viii) of second acid reaction in the hydrothermal treatment is carried out with phosphoric acid (H₃PO₄), involving formation of insoluble Mg phosphates, as can be observed in fig. 4.

It should be noted that observing the ratio between Mg/Si in a) and in b) there is an increase from about 0.6 to about 0.8. This last value, in particular, is in line with the ratio found by means of EDS analysis. This can be rationalized considering that the treatment method described here, leading to the breakdown of the layers of Si0₂, leads to the exposure of new layers of MgO, which are therefore at the origin of the XRF signal, further showing the effectiveness of the method described here. It is clear that modifications and/or additions of parts and/or steps may be made to the inertization method for materials containing asbestos as described heretofore, without departing from the field and scope of the present invention.

In particular, other embodiments of the method, combinable with all the embodiments described here, provide to carry out an intermediate grinding, that is to say that the filtered mass obtained after the reaction in a hot condition with the inorganic basic agent is subjected to grinding, before the reaction in a hot condition with the second inorganic acid agent. In particular, therefore, the second filtered mass obtained in step vii) can be subjected to grinding before carrying out step viii) with the second inorganic acid agent.

The Applicant has found that this grinding increases the effectiveness of the method described here with respect to the destruction of the asbestiform phase. The Applicant has found in experiments that a protracted grinding, in particular by means of a ball mill, helps the destruction of the fibers. As a consequence, in some embodiments the method provides to carry out a further grinding, preferably wet grinding, further with respect to the initial shredding and pulverization. This grinding can be preferentially carried out by means of a ball mill. The duration of the grinding is preferably not less than 60 minutes, in particular up to 5 hours, preferably between 2 and 4 hours. A preferential example is 3 hours. This grinding, although it can also be carried out dry, is preferably wet, with a concentration of solid from 20% (20% of solid, 80% water) to 80% (80% solid, 20% water). It should be noted that the term“solid” refers to dry powder, that is, the second filtered mass deriving from the filtration of step vii).

The grinding carried out between step vii) and step viii) is advantageous because it mechanically breaks down the asbestos fibers, as well as reducing the granulometry of all the other particles. During the grinding, advantageously with a ball mill, the fibers, as well as tending to reduce in diameter, above all gradually break down into fibers of increasingly smaller diameter, called “fibrils”. The Applicant has found that this phenomenon is very advantageous since it increases the exposed surface of the fibrous material, more open to the acid attack. For this reason, the grinding, in particular with a ball mill, is advantageous when carried out following the first basic hydrothermal reaction (step v), and therefore in this case after the filtration of step viii), before the acid hydrothermal reaction as in step viii).

The Applicant has carried out experimental tests using alumina grinding balls with a diameter of 32 and 14 mm with a ratio between the number of large and small balls of 1 :3. The weight of solid material, intended as dry powder, is about 25% of the weight of the grinding balls. It is clear that the setting of the ball mill can vary from situation to situation, adapted according to each case. This is because, depending on the quantity of water with respect to the solid, the weight and diameter of the grinding balls, the rotation speeds of the mill, for example, change. In general, the rotation speed has to be adjusted so that the centrifugal force of the rotation does not overcome the gravitational force acting on the grinding balls, since they would remain adhered to the wall of the mill during the rotation, but also so that it is not negligible, since the grinding balls would remain on the bottom of the mill, making the grinding process ineffective. Fig. 5 shows SEM photographs at 200, 500, 1000 and 2000 enlargements (respectively (a), b), c) and d)) after this grinding carried out after step vii) and before step viii). From the comparison of the images a), b), c) and d) of fig. 5, subjected only to comminution or pulverization, with the images a), b), c) of fig. 2 of the untreated material, we observe the substantial difference of the appearance of the material and the absence of fibers of large sizes. In the images c) and d) respectively at 1000 and 2000 enlargements of fig. 5, in particular we observe the presence of numerous fibrils, deriving from the mechanical destruction of larger fibers. In the image d) at 2000 enlargements we can still observe the presence of fibers of larger sizes, which survived the grinding step. However, we observe that these fibers appear much less branched with respect to the fibers of the pretreated material shown in fig. 2 a), b), c), suggesting that even in the case where the grinding does not lead to the shredding of the larger fibers, it has in any case an advantageous effect for the purposes of the destruction of asbestos.

In any case, this intermediate grinding operation supports the subsequent acid attack of step viii).

It is also clear that, although the present invention has been described with reference to some specific examples, a person of skill in the art shall certainly be able to achieve many other equivalent forms of inertization method for materials containing asbestos, having the characteristics as set forth in the claims and hence all coming within the field of protection defined thereby.

Claims

1. Inertization method for materials containing asbestos, said method comprising the following steps:

i) making available a powder of materials containing asbestos;

iii) neutralizing the pH of the mass reacted in ii);

vi) neutralizing the pH of the mass reacted in v);

ix) neutralizing the pH of the mass reacted in viii);

xii) neutralizing the pH of the mass reacted in xi);

2. Method as in claim 1, wherein said materials containing asbestos are cement- based materials containing asbestos, comprising, in a dry state, from 45 to 75% in weight, in particular from 50 to 70% in weight, of calcium carbonate, from 5 to 25% in weight, in particular from 10 to 20% in weight, of asbestos and from 20 to 50% in weight, in particular from 25 to 45% in weight, of silica.

3. Method as in claim 1 or 2, wherein said powder of materials containing asbestos has particle size D₈₀ of not more than 700 pm, in particular equal to or less than 500 pm.

4. Method as in claim 1, 2 or 3, wherein said powder of materials containing asbestos made available in step i) is in the presence of water, to supply it in wet form to the subsequent step ii).

5. Method as in any claim from 1 to 4, wherein said first inorganic acid agent of step ii) is hydrochloric acid and said second inorganic acid agent of step viii) is an acid chosen from a group consisting of: phosphoric acid, hydrochloric acid, sulfuric acid, nitric acid or hydrobromic acid.

6. Method as in any claim from 1 to 5, wherein said inorganic basic agent of step v) and said inorganic basic agent of step xi) are a base chosen from a group consisting of: sodium hydroxide, calcium hydroxide.

7. Method as in any claim from 1 to 6, wherein said reaction steps ii), v), viii) and ix) are carried out in reaction environments that are distinct and separate from one another.

8. Method as in any claim from 1 to 7, wherein in step ii) an exothermic reaction takes place initially at room temperature, while in steps v), viii) and ix) the reaction environment is kept hot at a temperature between about 200°C and 250°C.

9. Method as in any claim from 1 to 8, wherein said method provides to identify or know in advance the percentage content in weight of at least calcium carbonate or calcium hydroxide, asbestos and silica in the materials containing the asbestos to be treated, said method also providing to:

10. Method as in any claim from 1 to 9, wherein:

- in step ii) the weight ratio between dry mass of powder of materials containing asbestos made available in step i) and water ranges from 1 :0.5 to 1 :2 and the weight ratio between dry mass of powder of materials containing asbestos made available in step i) and aqueous solution of the first inorganic acid agent ranges from 1 : 1 to 1 :2;

- in step v) and in step xi) the weight ratio between dry mass of powder of materials containing asbestos made available in step i) and water ranges from 1 :10 to 1 :2 and the weight ratio of dry mass of powder of materials containing asbestos made available in step i) and inorganic basic agent ranges from 1 : 1 to 1 :0.05;

- in step viii) the weight ratio between dry mass of powder of materials containing asbestos made available in step i) and water ranges from 1 : 10 to 1 :2 and the weight ratio of dry mass of powder of materials containing asbestos made available in step i) and aqueous solution of the second inorganic acid agent ranges from 1 :0.1 to 1 : 0.5.

11. Method as in any claim from 1 to 10, wherein the second filtered mass obtained in step vii) is subjected to grinding, in particular wet grinding and/or in a ball mill, before carrying out the reaction of step viii) with the second inorganic acid agent.